Areolar connective tissue
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Areolar tissue is a common type of connective tissue, also referred to as "loose connective tissue". It is strong enough to bind different tissue types together, yet soft enough to provide flexibility and cushioning. It exhibits interlacing,[1] loosely organized fibers,[2] abundant blood vessels, and significant empty space. Its fibers run in random directions and are mostly collagenous, but elastic and reticular fibers are also present. Areolar tissue is highly variable in appearance. In many serous membranes, it appears as a loose arrangement of collagenous and elastic fibers, scattered cells of various types; abundant ground substance; numerous blood vessels. In the skin and mucous membranes, it is more compact and sometimes difficult to distinguish from dense irregular connective tissue. It is the most widely distributed connective tissue type in vertebrates.
It is sometimes equated with "loose connective tissue".[3] In other cases, "loose connective tissue" is considered a parent category that includes mucous connective tissue, reticular connective tissue and adipose tissue.[4]
Location
It may be found in tissue sections from almost every part of the body. It surrounds blood vessels and nerves and penetrates with them even into the small spaces of muscles, tendons, and other tissues. It may likewise be present in the mediastinal extremities. Nearly every epithelium rests on a layer of areolar tissue, whose blood vessels provide the epithelium with nutrition, waste removal, and a ready supply of infection-fighting leukocytes in times of need. Because the abundance of open, fluid-filled space, leukocytes can move about freely in areolar tissue and can easily find and destroy pathogens.
The areolar tissue is found beneath the dermis layer and is also underneath the epithelial tissue of all the body systems that have external openings.
It is also a component of the lamina propria of the digestive and respiratory tracts, the mucous membranes of reproductive and urinary systems, the stroma of glands, and the hypodermis of the skin.
Composition
It is a pliable, mesh-like tissue with a fluid matrix and functions to cushion and protect body organs.
Cells called fibroblasts are widely dispersed in this tissue; they are irregular branching cells that secrete strong fibrous proteins and proteoglycans as an extracellular matrix.
The cells of this type of tissue are generally connected by a gelatinous substance known as ground substance primarily made up of collagenous and elastic fibers.
Function
Areolar connective tissue holds organs in place and attaches epithelial tissue to other underlying tissues. It also serves as a reservoir of water and salts for surrounding tissues. Almost all cells obtain their nutrients from and release their wastes into areolar connective tissue.
Classification
Loose connective tissue is named based on the "weave" and type of its constituent fibers. There are three main types:
- Collagenous fibers: collagenous fibers are made of collagen and consist of bundles of fibrils that are coils of collagen molecules.
- Elastic fibers: elastic fibers are made of elastin and are "stretchable."
- Reticular fibers: reticular fibers consist of one or more types of very thin collagen fibers. They join connective tissues to other tissues.
Additional images
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Section of the human oesophagus. Moderately magnified.
References
- ^ "areolar tissue" at Dorland's Medical Dictionary
- ^ Template:EMedicineDictionary
- ^ "LOOSE CONNECTIVE TISSUE". Retrieved 2008-12-05.
- ^ "Blue Histology - Connective Tissues". Retrieved 2008-12-05.
External links
- Histology image: 43_07 at the University of Oklahoma Health Sciences Center - "Skin"
